Identification of proteins preferentially associated with the pMII-MAR plasmid. Mobility shift reactions with (+Ends) or without (–Ends) unlabeled 144 bp probe were separated in a preparative 1.5% agarose gel, pUC18 and MII plasmid bands excised, and proteins electroeluted as described in Materials and Methods. Proteins eluted from equal amounts (weight) of agarose were subjected to SDS–PAGE and western blot analysis. Western blots were probed with antibodies directed against DNA-PKcs and Ku86 (A), XRCC4 (B), SAF-A (C), DNA ligase IV (D), Topoisomerase II (E) or PARP (F). Lane 5 of (A)–(F) contained 25 µg of M059K nuclear extract. For clarity, lanes in western blots (B) and (F) were rearranged; however, each blot contained proteins from the same experiment treated under identical conditions. Proteins extracted from three independent mobility shift reactions produced similar band patterns.